This invention relates to a charged-particle energy analyzer. More particularly, it relates to a charged-particle energy analyzer for use in the surface analysis of a solid based on electron beams such as Auger electrons.
In analyzing a feeble electron beam of low energy such as Auger electrons and photoelectrons in the surface analysis of a solid, it is important to efficiently utilize the electrons emitted from the sample. To this end, the accepted solid angle (the solid angle of an electron beam entering an analyzer/the solid angle of an electron beam emitted from a sample) needs to be great.
As the optimum configuration for such a requirement, an analyzing system of a structure shown in FIG. 1 has already been proposed (Official Gazette of Japanese Open-laid Patent Application No. 96091/1977). This apparatus has a construction wherein a deflecting system consisting of two, inner and outer electrodes is arranged axially symmetrically around a sample, so that charged particles emitted from the sample and entering into the deflecting system draw a sharply curved track, whereupon they focus onto a center axis or onto a circumference with its center on the axis again. Behind the deflecting system, an analyzer is arranged at a position having such an electrooptical relation that the focus point is considered as the emission point of a signal. Thus, the detection of secondary electrons or the energy analysis of photoelectrons, Auger electrons etc. is effected.
Referring to FIG. 1, numeral 1 designates an electron gun. An electron beam 2 generated therefrom is focused by a focusing lens 3, and is focused on a sample 4. Charged particles 5 such as secondary electrons and Auger electrons are emitted from the irradiated point of the sample 4 in a spacial distribution conforming substantially with the cosine law. Among the charged particles, an electron flux surrounded between two cones whose vertices lie at point P and which have half vertical angles of .theta.+ a and .theta.- a respectively enter the interspace between deflecting electrodes 6 and 7. The deflecting electrodes 6 and 7 constitute a double electrode system which is axially symmetric and which has an L-shaped section.
The charged particle flux is advanced along a sharply curved track by a deflecting electric field in the deflecting electrode system. Further, it has the track corrected by an auxiliary electrode 8 and converges on a slit 9 posterior to the auxiliary electrode 8 in the first order of the very small angle a. After passing through the slit 9, it advances so as to cross on a center axis. The charged particle flux is subjected to an energy analysis by a cylindrical mirror type analyzer 10 arranged in the next stage, and only the charged particles having certain specified energy converge on a detecting slit 9' located on the axis. A signal is detected by a detector 11 which is disposed behind the detecting slit 9'.
Voltages which are applied to the respective electrodes of the deflecting electrodes 6 and 7, the auxiliary electrode 8 and the cylindrical mirror type analyzer 10 are appropriately selected with power sources 12, 13 and 14, and the applied voltage values are thereafter scanned at a fixed ratio. Then, in case of e. g. the Auger electron analysis, the electron energy spectrum emitted from the sample can be obtained because the electron track depends upon the energy.
In the above, the analysis of Auger electrons emitted from the sample has been described as an example. In this case, a switch S.sub.1 located at a stage succeeding to the detector 11 is kept thrown onto an A side. The detected signal is amplified by a lock-in amplifier 15, and is subjected to a sensitive phase detection by the use of a perturbation A. C. at a frequency f. When the amplified signal is recorded by a recorder 16, the Auger electron energy spectrum can be obtained here.
On the other hand, the power sources 12, 13 and 14 are fixed at predetermined voltage values so as to detect only Auger electrons having specified energy. Under this state, the switch S.sub.1 is kept thrown onto a B side, a deflecting coil 19 of a cathode-ray tube 20 and a deflecting coil 18 for the primary electron beam are synchronously driven by a power source 17, the primary electron beam is scanned on the sample, and the intensity of the signal which is produced in correspondence with the scanned position of the sample surface and which responds to the Auger electrons of the specified energy value is used for the brightness modulation of the CRT 20. Then, an Auger electron scanning image of a specified element corresponding to the scanning area of the primary electron beam can be displayed on the screen of the CRT 20.
The foregoing description has been made of the operating procedures of the ultrahigh sensitivity Auger electron analyzer which has heretofore been used. With the prior-art method, the signal charges emitted from the sample are detected from all directions, and hence, it is difficult to discriminate whether the intensity of the detected signal is truly founded on the quantity of the element contained in the sample or it is related with the shape (concave or convex condition) of the sample surface in the measured place.